Field of the Invention
The invention relates to a lens unit and an optical device such as a digital camera, which is equipped with the lens unit.
Description of the Related Art
Lens barrels mounted in optical devices such as digital cameras include a zoom type which changes shooting magnifications by moving a plurality of lenses constituting a shooting optical system in a direction of an optical axis between a retracted position and a shooting position. Lens barrels of the zoom type are required to move the plurality of lenses in the direction of the optical axis while holding the plurality of lenses in a rotation-inhibited state with high accuracy.
Due to a recent demand for reducing the cost of cameras, lens barrels having plastic lenses in place of glass lenses are increasingly used. On the other hand, as cameras are increasingly downsized, a technique to efficiently combine a plurality of plastic lenses, which are small, easy to assemble, and inexpensive, and hold them with high accuracy is required.
Examples of conventional lens holding structures include a proposed structure in which an outer periphery of a glass lens is fitted and held in a concave portion, which is formed in a plastic lens, in a direction of an optical axis (the specification of U.S. Pat. No. 6,819,508). Also, there has been proposed a structure in which a tapering convex portion formed in one of two plastic lenses is fitted and held in a tapering concave portion, which is formed in the other one, in a direction of an optical axis (the publication of U.S. Pat. No. 4,959,183).
According to the specification of U.S. Pat. No. 6,819,508 stated above, however, the lens fitted into the concave portion formed in the plastic lens is made of glass, and no mention is made of how to deal with a gate for use in molding of the plastic lens.
Moreover, according to the publication of U.S. Pat. No. 4,959,183 stated above, for each of the two plastic lenses, a flange portion is provided over the whole circumference of a fitting portion on an outer side in a radial direction, and a gate is disposed in this flange portion. This increases the outer diameters of the plastic lenses accordingly to bring about an increase in the size of the lens barrel.